The invention relates to improvements in leads which are utilized to connect a cardiac pacemaker with an electrode in the heart, e.g., with a corkscrew-shaped or tip-shaped electrode which is anchored in a wall of a patient's heart. Still more particularly, the invention relates to improvements in cardiac pacemaker leads of the type wherein an elongated flexible catheter carries an electrode at its distal end and defines a passageway for an elongated flexible stylet in the form of a wire or the like.
Cardiac pacemaker leads of presently known design are constructed to implant any one of a variety of different electrodes in the heart of a patient. The electrode can resemble a corkscrew, a so-called tip, an umbrella, a pronged structure or a device having bristle-like projections which serve to anchor the electrode in the tissue of a wall in the heart. Reference may be had, for example, to commonly owned German patent application No. 25 39 553 (published Mar. 10, 1977) which shows a cardiac pacemaker lead with an electrode in the form of a corkscrew. Commonly owned German Pat. No. 31 46 182 (application published Jun. 1, 1983) discloses a lead with a substantially umbrella-like electrode.
Cardiac pacemaker leads of the above outlined character exhibit the advantage that the electrode can be firmly and reliably implanted in the tissue of a wall in the heart of a patient. This is desirable and advantageous in order to ensure predictable stimulation when the pacemaker is in use. However, conventional leads also exhibit a serious drawback, namely that the electrode and the remainder of the lead cannot be readily withdrawn from a patient's body, e.g., after several months or after several years of use when such removal is dictated by infection or for any other reason. Therefore, it is often necessary to resort to open heart surgery with attendant problems involving trauma, danger of infection and extremely high cost.
Heretofore known attempts and proposals to extract a cardiac pacemaker lead without surgery involve the application of a pull to the proximal end of the lead, i.e., to that end which is connected to the pacemaker and is readily or reasonably readily accessible to a physician. A drawback of such proposal is that the lead is likely to break or tear since the major part of the lead normally consists of convoluted wire which is often surrounded by an insulating sheath of plastic material. Neither the coiled wire nor the sheath is capable of standing tensional stresses of a magnitude which is necessary to extract a properly implanted cardiac pacemaker lead several months or years after implantation.
In order to reduce the likelihood of breakage or tearing of a standard cardiac pacemaker lead, additional proposals include the provision or utilization of rollers or weights which are affixed to the proximal end of the lead and remain affixed for a period of several days to ensure gradual extraction of the electrode and distal end of the lead from the heart of a patient. Such mode of extracting the electrode and the entire lead is a hit-and-miss proposition so that it is normally, or at least often, followed by surgery. Moreover, the application of a constant pull for an extended period of time can result in separation of the distal end from the remaining major portion of the implanted lead so that the removal of the distal end necessitates an open heart surgery.
European patent application No. 0 47 013 of Stokes (published Mar. 10, 1982) discloses a body implantable lead which is designed to deliver stimulation energy to a heart or another body site. The distal end or head of the lead is provided with rearwardly inclined tines which ensure reliable anchoring of the head into the tissue. This lead exhibits the same drawbacks as the aforediscussed leads.
European patent application No. 0 368 568 of Goode et al. (published May 16, 1990) discloses a heart lead removal apparatus. The apparatus employs a stylet with an expandable member which is inserted in the coiled structure of the lead. A drawback of such proposal is that the exertion of a pull upon the coiled structure can result in separation of the coiled structure from the distal end of the lead.
European patent application No. 0 282 047 of Bisping (published Sep. 14, 1988) discloses a flexible lead wherein a coil spring in the distal end is caused to store energy which can be dissipated for the purpose of withdrawing a corkscrew-shaped electrode from body tissue. Such dissipation of energy is initiated in response to axial displacement of a piston in the distal end of the lead.